Field of the Invention
The present invention relates to a two-member connecting structure for connecting via a lock ring a first member, which is provided with a first lock groove in an outer periphery of the first member, and a second member, which includes a connection hole permitting insertion of the first member therethrough, the second member being provided with a second lock groove opened to an inner periphery of the connection hole, and the lock ring being formed in a substantially C shape while having a circular section, and engaging with the first and second lock grooves.
Description of the Related Art
As for a decompression valve, Japanese Patent Application Laid-open No. 2014-10784 has made known a connecting structure for connecting via a lock ring a holding plate as a first member, which is provided with a first lock groove in its outer periphery, and a diaphragm rod as a second member, which includes a connection hole permitting insertion of the holding plate therethrough, and which is provided with a second lock groove opened to an inner periphery of the connection hole, the lock ring being formed in a substantially C shape while having a circular section, and engaging with the first and second lock grooves. The configuration of the connecting structure is as follows. When the lock ring is in engagement with the second lock groove, a half or more of the section of the lock ring is inside the second lock groove. When the holding plate and the diaphragm rod are acted on by external force which separates the holding plate and the diaphragm rod from each other, force in an axial direction which is part of force acting on the lock ring from the holding plate is received by a side surface, located on an open end side of the connection hole, which is one of the opposite side surfaces of the second lock groove in the axial direction, and force in a direction perpendicular to the axial direction is received by a groove bottom surface of the second lock groove. Movement of the lock ring is restricted by the one side surface of the second lock groove and the groove bottom surface. Thereby, the holding plate and the diaphragm rod are kept connected to each other.
Furthermore, an outer diameter of the lock ring under a load-free condition where no external force acts on the lock ring is set larger than a diameter of the groove bottom surface of the second lock groove which is opened to the inner periphery of the connection hole. When the holding plate is inserted into the connection hole with the lock ring engaging with the first lock groove, the lock ring comes into contact with an inner periphery of a part of the connection hole which is located short of the second lock groove in an insertion direction of the holding plate into the connection hole, and thus reduces its diameter. When the lock ring reaches the second lock groove, the lock ring increases its diameter, and engages with the second lock groove. Thereby, the holding plate is connected to the diaphragm rod.
In the connecting structure disclosed in Japanese Patent Application Laid-open No. 2014-10784, however, a depth from an inner peripheral surface of the part of the connection hole, which is located short of the second lock groove in the insertion direction of the holding plate into the connection hole, to the groove bottom surface of the second lock groove is larger than a radius of the circular section of the lock ring. When the holding plate and the diaphragm rod are connected together, the diameter of the lock ring needs to be largely reduced from a diametrical dimension of the circular section of the lock ring. For this reason, larger force is needed to insert the holding plate into the connection hole while reducing the diameter of the lock ring, and ease of assembly is degraded. Furthermore, if the lock ring is deformed into a plastic deformation range, there is likelihood that: the lock ring no longer returns to the original outer diameter even under a load-free condition; and an engagement failure occurs so that strength of connection between the holding plate and diaphragm rod decreases.